Funds are requested to support the development and pilot testing of a brief intervention (The Teen Marijuana Check-Up) with non-treatment seeking adolescent marijuana users. The intervention is a motivational enhancement treatment consisting of three individual sessions, all of which are delivered in the school setting. The participant is first assessed regarding use of marijuana, alcohol, and other drugs, as well as pertinent attitudes and goals. In the second and third sessions, a personalized feedback report containing information from the participant's assessment, as well as normative comparison data, is reviewed, with the health educator employing motivational interviewing strategies intended to enhance motivation for reduction or cessation of marijuana use. Specific goals for change and behavior change strategies are discussed with participants who wish support to change their marijuana use. The primary aim will be to determine if an efficacy trial with this intervention is warranted. As such, this proposal includes the following as specific aims: (1) to revise and manualize a three-session motivational enhancement intervention for delivery in high schools to adolescents who smoke marijuana frequently; (2) to revise and manualize participant recruitment mechanisms; (3) to develop and pre-test a computer-assisted self-interviewing assessment system for this population; (4) to modify process and outcomes measures concerning the hypothesized effects of the experimental intervention; (5) to develop a training protocol for the experimental intervention; (6) to develop measures of health educator competence and adherence; (7) to develop measures of intervention fidelity; (8) to conduct a pilot study in which effect sizes for key outcomes are determined; (9) to describe self-referred participants vs. those referred by others with reference to: baseline marijuana, alcohol, and other drug use patterns; baseline indicators of problematic consequences of use; indicators of comorbidity; intervention completion; and research retention; (10) to measure participant evaluations of the study's recruitment, assessment, and intervention components; and (11) to measure evaluations by key school personnel (e.g., counselors, intervention specialists) of the study's implementation and impact within the participating schools.